1. Field of the Invention
The invention relates to the field of optics. More particularly, the invention relates to video cameras. In still greater particularity, the invention relates to variable magnification video cameras. By way of further characterization, but not by way of limitation thereto, the invention relates to a variable magnification video camera achieved by mechanically stopping down the aperture size of the lens to allow variable magnification.
2. Description of the Related Art
Individuals with vision impairment have long sought aids to assist them in reading and performing other functions necessary in daily life. Many types of visual impairment caused by retinal deterioration are present in these individuals. One form of visual impairment is known as macular degeneration. Macular degeneration primarily occurs in elderly people and prohibits them from reading books or newspapers, etc. as well as labels, prescriptions, or other items which by necessity are desirable for a comfortable standard of living. Optical magnifying devices of many types have been used by these individuals to assist in these necessary functions. However, as retinal deterioration progresses, the limitations on magnifying capability limit the usefulness of these devices.
Video reading systems have become available in recent years. That is, the introduction of video cameras has made closed-circuit television devices useful to enable individuals with visual impairment such as macular degeneration to function normally. These devices magnify and enhance text or even photographs by displaying them greatly magnified on a video screen. This enables vision impaired individuals to more easily read text or view images. Available equipment ranges from small hand-held portable-type devices to large, fixed devices with variable magnification into which the object or text to be viewed is placed. For many of these individuals, the small hand-held portable devices are more desirable. However, these devices tend to be more limited in the functions which they are capable of performing. In particular, the ability to change magnification in the hand held devices is accomplished only through physically changing lenses or changing to a camera with a different lens. The ability to quickly change magnification is important for ease of use and because the text or image to be viewed may vary in size from word-to-word or line-to-line.
An example of a small hand-held video reading device is presently being marketed under the trademark Easy-Reader. This device is available in three fixed focused lens/camera options of 10 power, 20 power or 30 power. The device uses a video camera with a clear plastic extension which is placed against the text or image to be read. The clear plastic extension allows ambient light to fall upon the object to be magnified and allows the user to keep the camera the correct distance from the text or image to maintain correct focus of the text or image. Such a device is less expensive than a device such as the Chroma CCD offered by Telesensory, Inc. of Mountain View, Calif. The Chroma CCD model includes a fixed viewing system into which the item to be read is placed. The device then displays the image on a video monitor. Variable magnification is accomplished by adjusting a knob which controls a zoom lens in the viewing system. Each change of magnification generally requires refocusing unless the device is first very carefully focused at the highest magnification level, a practice which low vision users find difficult. This device offers the advantage of variable magnification as opposed to the Easy Reader-type device. However, while suited for its intended purpose, this device requires refocusing, is more cumbersome to use, and is significantly more expensive. That is, the unit is not hand-held or as portable as the Easy Reader device and is two or three times as costly. It would be desirable to have a relatively inexpensive, hand-held device which allows variable magnification for the visually impaired user.